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My Solar Bicycle

I am anticipating peoples’ reactions:

“Why do you have solar panels on your bicycle?”

“What do you do when it rains?”

“Can the solar panel drive the electric motor directly?”

“Did you make it yourself?”

“What the…”

Allow me to explain. My vehicle of choice is a “stoked Xtracycle”. (For those of you not “in the know”, an Xtracycle is a type of cargo bike that has an extra long frame. And “stoked” means that my bike has a Stokemonkey electric motor that helps me out on the hills.) In general this summer I’ve been biking 10 to 20 miles a day and then recharging my battery overnight by simply plugging it into an outlet. However, next week I’m going on a 3-day 240-mile camping trip through the Adirondacks where I might not have access to an outlet. The solar panels will help extend the range of my bicycle. So to answer your questions:

“Why do you have solar panels on your bicycle?”

I use them to extend the range of my electric cargo bike for long trips (plus they were fun to make). I will carry two batteries on my trip, each giving my bike a range of 20 to 40 miles. On a sunny day the solar panels can recharge one of the batteries while I am riding, adding an additional 20 to 40 miles for a total range of 60 to 120 miles a day. I anticipate some hills and I’ll be carrying a load, so a 60-mile range is probably more accurate. I may need to pedal the last few miles on some days.

“What do you do when it’s cloudy or it rains?”

I plan to stay in a hotel some of the time and recharge my batteries there.

“Can the solar panel drive the electric motor directly?”

Not really. The solar panels don’t produce enough electricity instantaneously. For example the solar panels only produce about 40 watts of power at a given moment, whereas my bicycle needs about 400 watts of power to go up a hill. The main purpose of the solar panels is to charge the battery over time. Since charging happens slowly, 40 watts is enough to charge the battery. It takes roughly 10 hours of charging to store one to two hours’ worth of electrified riding time in the battery. And one to two hours of riding translates into 15 to 30 miles.

“Did you make it yourself?”

I already had the stoked Xtracycle, which is described on my About This Bike page. As you can read there, an electric cargo bike can be had for $1000 to $3500. And I had already constructed the canopy frame for a previous project, the Bike Wagon Canopy ($150). I found the canopy was somewhat wobbly with the weight of the solar panels so I had to strengthen it with guy wires. It remained for me to add the solar panels and the electronics. I used maritime-grade solar panels that were designed to keep sailboat starter batteries charged up, so they are extra-sturdy and consequently somewhat expensive. I’ve since seen panels with almost twice the power at 3/4 the price. Cost of panels: $900 to $1200. I am using three 12-volt panels in series to produce the 36 volts required by my battery. I spent a lot of time researching what sorts of electronics I would need between the panels and the battery, and finally concluded that I can just plug the panels into the battery directly. (I plan to write more about this in a later post.)

Total cost for a solar bicycle: $2050 to $4850. Not bad for a vehicle that can get you both out of the car and off the grid.